Patent GB-458823-A (GB)
Title: A new or improved automatic control system, utilising fluid pressure
IPC: G01D5/42
Filed: 1935-06-25
Abstract: 458,823. Fluid-pressure servomotorcontrol systems. KENT, Ltd., G., 199, High Holborn, London, and HOWARD, G. P. E., and IVANOFF, A., Biscot Road Works, Luton, Bedfordshire. June 25, 1935, No. 18206. [Class 135] In a fluid-pressure servomotor-control system arranged for alternative automatic or manual control, the pressure on the pressure responsive device operating the valve or other member to be controlled is automatically maintained constant during a change from one form of control to the other so that no discontinuity in the pressure occurs and sudden movements of the member to be controlled are avoided. When a change of the form of control is made, a member such as the lever 38, responsive to the difference between the fluid-pressure transmitted by the form of control operative before the change-over and the pressure due to the setting of the form of control to be operative after the change-over, operates, in accordance with the magnitude of the response, regulating means such as the piston 19 operating in the cylinder 20, which adjust the said setting so that the pressure transmitted by the control which is subsequently operative is the same as that transmitted before the change-over. As shown, the fluid-pressure in a pipe 4 and a bellows 1 is controlled automatically by changes in a variable condition. The bellows 1 is connected by a link 3 to an opposed bellows 2 communicating by a pipe 5 with the fluid-pressure responsive device operating the valve. The link 3 is coupled by an arm 14 to a lever 15 bearing a slidable weight 17. A pivoted vane 9 coupled to the link 3 controls the supply of pressure fluid through conduits 11, 13, 5 to the bellows 2, the pressure in which at each instant balances the fluid-pressure in the bellows 1 and the load 17. The conduit 5 also communicates by a pipe 42 with a second pair of opposed bellows 35, 36, the connecting link 37 of which is coupled to a pivoted vane 28 controlling the piston 19 and regulating the position of the load 17. In changing from automatic to manual control, the bellows 1 is vented to atmosphere by operation of a cock 32, cocks 43, 44 in the pipes 42, 5 respectively are closed, and a cock 34 controlling the pressure fluid supply for the piston 19 is opened. The four cocks 32, 43, 44 34 are preferably operated by a single operating member. The pressure isolated in the bellows 35 corresponds to that in the bellows 2 when the change-over is made. As the bellows 1, 2 no longer balance, the vane 9 is moved to change the pressure in the bellows 2 and hence also in the bellows 36 to restore the balance. The bellows 35, 36 are thus thrown out of balance and operate on the vane 28 so that the piston 19 moves the load 17 to compensate for the pressure loss in the bellows 1. Finally, a state of equilibrium is reached in which the pressure in the bellows 2, 36 again equals that in the bellows 35. The cocks 43, 44 may then be opened and the cock 34 closed. The cock 32 is not altered. The valve or other regulating member may then be controlled solely by manual adjustment of the load 17. In changing back from manual to automatic control, the cocks are operated as before with the exception of the cock 32 which is opened to the automatic control pressure and remains so opened. A simpler form is also described in which the bellows 35, 36 are dispensed with, the vane 28 being linked to the lever 15 and operated thereby when the bellows 1, 2 are thrown out of balance. In this case, the pressure in the bellows 2 is isolated by a cock in the pipe 13.